JP5226592B2 - Limit load prediction method for resin molded parts with stress concentration - Google Patents

Description

  The present invention predicts the generated stress generated in the stress concentration part of the resin molded product when a load that breaks the resin molded product having a shape stress concentration part is applied, and limits it based on the predicted generated stress. The present invention relates to a method for predicting a load.

  Many resin materials are excellent in thermal properties and mechanical properties, and are used in various fields because of their advantages such as light weight. In recent years, improvements to improve the physical properties of materials have been actively performed. As a result, resin materials are used in various environments.

  As described above, a resin molded product made of a resin material is used in various scenes, and depending on the scene where it is used, a very high mechanical strength may be required. In order to meet such a requirement, for example, a resin composition for obtaining a resin molded article having excellent mechanical strength such as a thermoplastic resin described in Patent Document 1 is disclosed.

  It is also important to improve the resin material and improve the mechanical strength of the resin molded product as described above, but when improving or selecting the resin material, the specified resin material was actually applied to the resin part. In this case, if it is possible to predict in what direction and how much load the resin part can withstand, it becomes easy to improve the resin material, and it becomes easy to select the resin material.

JP 2008-1744 A

  However, many resin parts have complicated shapes, and when a predetermined load is applied to the resin parts, there are many cases where stress is concentrated preferentially and the thickness and width are easily damaged. . A portion where stress concentrates as described above when a load is applied and the thickness and width are greatly deformed is referred to as a stress concentration portion. When a load is applied to a resin molded product having a stress concentration portion, it is extremely difficult to predict how much stress is generated in the stress concentration portion. For this reason, there is no disclosure of a method for accurately predicting up to what load a resin molded product having a stress concentration portion can withstand.

  The present invention has been made in order to solve the above-described problems. The purpose of the present invention is to form a resin molding when a load is applied to a resin molded product having a shape stress concentration portion and the resin molded product breaks down. In the product, the stress concentration portion is broken, but the stress generated in the stress concentration portion is predicted more accurately, and a limit load prediction method is provided.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the stress measurement resin test piece of the stress measurement resin test piece when a load is applied to the stress measurement resin test piece of a predetermined ambient environment that does not have the shape stress concentration part, and the shape stress concentration part A correction coefficient obtained by dividing the predicted limit load calculated from the analytical stress generated in the stress concentration part obtained by analysis when a load is applied to the resin molded product provided by the actual measured limit load obtained by actual measurement, and In addition, for a strain measurement resin test piece at a predetermined temperature that does not have a stress concentration portion, it is found that there is a correlation between the strain at break when a load is applied in the tensile direction to the strain measurement resin test piece, The present invention has been completed. More specifically, the present invention provides the following.

  (1) Predict the stress generated in the stress concentration part of the resin molded product when a load that breaks the resin molded product having a shape stress concentration part is applied, and limit the resin molded product having the stress concentration part A stress prediction method for deriving a critical stress of a stress measurement resin test piece when a load is applied to a stress measurement resin test piece in a predetermined surrounding environment that does not have a shape stress concentration portion. A derivation step, and a rupture strain derivation step for deriving a rupture strain when a load is applied in the tensile direction to the strain measurement resin test piece with respect to a strain measurement resin test piece of a predetermined temperature not provided with a stress concentration portion; An analysis stress deriving step of deriving analytical stress generated in the stress concentration portion by analysis when a predetermined load is applied to a stress concentration resin test piece having a stress concentration portion having a predetermined radius of curvature; Analytical stress A predicted limit load calculation step of calculating a predicted limit load by dividing the limit stress using the analytical stress per unit load calculated from the above, and the stress concentration resin test piece in the stress concentration resin test piece is broken An actual measurement limit load deriving step for deriving an actual measurement limit load, a correction coefficient deriving step for obtaining a correction coefficient by dividing the predicted limit load using the actual measurement limit load, the type of resin material and / or the Correlation deriving step of changing the predetermined ambient environment and performing the step of obtaining the correction factor at least once in the same manner as the correction factor deriving step and deriving the correlation between the fracture strain and the correction factor by a function of a predetermined form And an estimated correction coefficient determination step of determining an estimated correction coefficient based on the correlation between the fracture strain and the correction coefficient.

（式（Ｉ）中のｙは補正係数、ｘは破断歪み、ａは係数、ｎは定数を表す。） (2) The limit load prediction method according to (1), wherein the function of the predetermined format satisfies the following formula (I).

(In formula (I), y represents a correction coefficient, x represents a breaking strain, a represents a coefficient, and n represents a constant.)

  (3) The correlation derivation step is performed by changing the radius of curvature and performing the step of deriving the correlation with the function of the predetermined format at least once in the same manner as the correlation derivation step. The limit load prediction method according to (1) or (2), further comprising a step after the step.

  (4) The limit load prediction method according to any one of (1) to (3), further including a relational expression deriving step for deriving a relation between a constant and a radius of curvature in the function of the predetermined format.

（式（ＩＩ−ａ）中のａは係数、Ｒは曲率半径、ｃ_１、ｄ_１は定数を表す。）

（式（ＩＩ−ｂ）中のｎは定数、Ｒは曲率半径、ｃ_２、ｄ_２は定数を表す。） (5) The limit load prediction method according to (4), wherein the relationship between the constant and the radius of curvature in the function of the predetermined format satisfies the following formulas (II-a) and (II-b).

(In formula (II-a), a is a coefficient, R is a radius of curvature, and c ₁ and d ₁ are constants.)

(In formula (II-b), n is a constant, R is a radius of curvature, and c ₂ and d ₂ are constants.)

  (6) The stress measurement resin test piece is the same as the strain measurement resin test piece, and in the limit stress deriving step, the limit stress is derived by applying a load in the tensile direction. The limit load prediction method according to any one of (5).

  (7) The limit load prediction method according to any one of (1) to (6), wherein the analysis is a linear analysis.

  (8) The estimated correction coefficient determination step is a step of calculating an estimated correction coefficient based on the fracture strain and the radius of curvature using the relational expression derived by the method described in (4) or (5), Generated stress prediction that predicts the generated stress in the stress concentration part of the resin molded product with a geometric stress concentration part by multiplying the estimated correction coefficient by the analytical stress when a desired load is applied to the resin molded product And a step of predicting a limit load.

  (9) The limit load characterized by calculating the limit load of the resin molded product by dividing the limit stress by the generated stress predicted by the method described in (8) and multiplying by the desired load. Prediction method.

  According to the present invention, when a load is applied to a resin molded product having a shape stress concentration portion, and the resin molded product breaks, the resin molded product breaks the stress concentration portion, but the stress concentration portion is generated. The stress can be predicted more accurately, and the limit load can also be predicted more accurately based on the generated stress obtained by the above prediction.

It is a figure which shows the resin test piece provided with the shape stress concentration part which has a notch on both sides. It is a figure which shows the resin test piece which is not provided with a shape stress concentration part. It is a figure which shows the resin test piece provided with the shape stress concentration part with a notch on one side. It is a figure which shows the L-shaped resin test piece provided with a stress concentration part. It is a figure which shows the power approximation function (y = ax- ⁿ ) which should represent the relationship between a correction coefficient and a fracture | rupture distortion. It is a figure which shows multiple correlation with a correction coefficient and a fracture | rupture distortion. Coefficient of a predetermined format function _{(a 1,} a _2), a diagram showing the relationship between constants _(n 1, _{n 2)} and the radius of curvature (R). It is a figure which shows the relationship between the curvature radius and correction coefficient in each destruction mode. It is a figure which shows the resin test piece used in the Example. It is a figure which shows the measuring method of the critical stress of an Example. It is a figure which shows the resin molded product used in the Example.

  Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the following embodiment, and may be implemented with appropriate modifications within the scope of the object of the present invention. it can.

<Limit load prediction method>
The present invention predicts the generated stress generated in the stress concentration portion of the resin molded product when a load that causes the resin molded product having a geometric stress concentration portion to break is applied, and predicts the limit load of the resin molded product It is a method to do. The limit load prediction method of the present invention derives the limit stress of the stress measurement resin test piece when a load is applied to a stress measurement resin test piece of a predetermined ambient environment that does not have a shape stress concentration portion. Limit stress derivation step and rupture strain derivation step for deriving the rupture strain when a load is applied to the strain measurement resin test piece in the pulling direction for a strain measurement resin test piece having a predetermined temperature without a stress concentration portion. And an analytical stress deriving step of deriving analytical stress generated in the stress concentration portion by analysis when a predetermined load is applied to a stress concentration resin test piece having a stress concentration portion having a predetermined radius of curvature. A predictive limit load calculating step of calculating a predictive limit load by dividing the limit stress using the analytical stress per unit load calculated from the analytical stress, and the stress concentration resin test piece An actual limit load deriving step for deriving an actual limit load when the stress-concentrated resin specimen breaks, and a correction coefficient deriving step for obtaining a correction coefficient by dividing the predicted limit load using the actual limit load, Change the type of the resin material and / or the predetermined surrounding environment, and perform the step of obtaining the correction coefficient at least once in the same manner as the correction coefficient derivation step, and the correlation between the fracture strain and the correction coefficient in a predetermined format. A correlation deriving step derived by a function; and an estimated correction coefficient determining step of determining an estimated correction coefficient based on the correlation between the fracture strain and the correction coefficient. After determining the estimated correction coefficient, for example, by multiplying the analytical stress when a desired load is applied to the resin molded product by the estimated correction coefficient, the stress concentrated part of the resin molded product having a shape stress concentration part A generated stress prediction step for predicting the generated stress generated in the step, and a limit load prediction step for calculating the limit load of the resin molded product by dividing the limit stress by the generated stress and multiplying by the desired load. By doing so, the limit load can be predicted. Hereinafter, an example of the limit load prediction method of the present invention will be described.

[Determination of resin material]
The present invention can be applied to all resin materials. A resin mixture obtained by blending a plurality of resin materials is also included in the resin material. In addition, additives such as nucleating agent, carbon black, pigments such as inorganic fired pigments, antioxidants, stabilizers, plasticizers, lubricants, mold release agents, and flame retardants are added to the resin to achieve desired characteristics. The applied resin composition is also included in the resin material. Therefore, the resin material used as the raw material of a desired resin molded product becomes a resin test piece or a resin material.

[Molding of resin material]
After selecting the resin material, the resin material is molded. The molding method is not particularly limited, and examples thereof include various molding methods such as compression molding, transfer molding, injection molding, extrusion molding, and blow molding. The resin material thus molded becomes a resin test piece.

[Limit stress derivation process]
The critical stress derivation process is the critical stress generated at the fracture location of the stress measurement resin test piece when a load is applied to the stress measurement resin test piece in a predetermined ambient environment that does not have a shape stress concentration part. Is a process of deriving. The critical stress refers to a fracture stress in a resin material that exhibits a brittle fracture mode, and a yield stress in a resin material that exhibits a ductile fracture mode, and means a stress that is a strong usage limit in the resin material.

  The method for measuring the limit stress is not particularly limited, and can be measured by a conventionally known method. For example, when the critical stress is measured by bending a resin test piece, it can be measured using a general bending tester, and when the critical stress is measured by pulling the resin test piece in the pulling direction. The critical stress can be measured using a general tensile testing machine.

  A “stress concentration part” is a part where stress is preferentially concentrated over other parts when a load is applied to the resin test piece, and is easily damaged. In this case, the thickness and width of the resin test piece are greatly changed as compared with other portions in the resin test piece. The “formal stress concentration part” refers to a resin test piece provided with a dent, a groove, a thin part, and the like. For example, a resin test piece as shown in FIG. When the resin test piece of FIG. 1 (a) is pulled in the pulling direction (in the direction of the white arrow) as shown in FIG. 1 (b), stress is concentrated in the stress concentration portion as shown in FIG. 1 (b). Stress is applied in the direction of the arrow.

  In addition, the “resin test piece not including a shape stress concentration portion” includes, for example, a resin test piece as shown in FIG. When the resin test piece of FIG. 2 (a) is pulled in the pulling direction (in the direction of the white arrow) as shown in FIG. 2 (b), the stress is applied in the direction of the arrow as shown in FIG. 2 (b). It takes evenly.

  By using a resin test piece that does not have a shape stress concentration part, when a load is applied to the resin test piece, the stress applied to the broken portion of the resin test piece can be measured more accurately. As a result, the critical stress of the resin material can be derived more accurately. Note that. As described above, the reason for using the resin test piece that does not include the shape stress concentration portion is to obtain the limit stress more accurately.

  “Ambient environment” refers to temperature and atmosphere (air, water, fuel, etc.). The value of the critical stress derived when the surrounding environment is different also differs. Therefore, the property of the resin molded product cannot be accurately predicted unless the ambient environment is determined as a predetermined ambient environment and analysis stress described later is not performed in the similar ambient environment. However, the predetermined ambient environment includes those having different conditions in the ambient environment to such an extent that the effects of the present invention are not impaired.

[Breaking strain derivation process]
The breaking strain deriving step derives the breaking strain when a load is applied to the strain measuring resin test piece in a tensile direction with respect to the strain measuring resin test piece having a predetermined temperature that does not have a shape stress concentration portion. It is a process. Strain measurement The amount of strain of the resin test piece when a load is applied in the tensile direction to the resin test piece will vary if the temperature of the resin test piece differs, so it is necessary to measure the strain at a predetermined temperature. is there. The predetermined temperature is the same condition as the temperature included in the predetermined ambient environment.

  Breaking strain refers to the amount of strain until breakage occurs when the above load is applied to a resin test piece. The breaking strain of the resin test piece can be expressed by elongation (%) until the resin test piece breaks using a conventionally known tensile tester.

  The breakage strain measurement test piece is a resin test piece that does not have a shape stress concentration portion like the stress measurement resin test piece. For this reason, if it is the measuring method of the limit stress using a tensile testing machine, a fracture | rupture distortion can be measured simultaneously. By measuring these simultaneously, it is possible to easily derive a relationship between a correction coefficient and a fracture strain described later.

[Analysis stress derivation process]
The analysis stress deriving step is a step of deriving by analysis the stress generated in the stress concentration portion when a predetermined load is applied to a stress concentration resin test piece having a stress concentration portion having a predetermined radius of curvature. It is.

  “Stress concentration resin test piece having a stress concentration portion having a predetermined radius of curvature” means, for example, a resin test piece having notches on both sides as shown in FIG. 1A, as shown in FIG. 3A. A resin test piece having a notch on only one side, and an L-shaped test piece as shown in FIG. In these test pieces, stress is concentrated at the front end portion of the notch or the L-shaped corner portion, and these portions have a predetermined radius of curvature.

  When stress is applied to the stress-concentrated resin test piece having notches on both sides as shown in FIG. 1 (a), as shown in FIG. Stress is applied to the part in the direction of the arrow as described above. When a stress is applied in the pulling direction (in the direction of the white arrow) as shown in FIG. 3B to a stress concentration test piece having a notch on one side as shown in FIG. Is stressed in the direction of the arrow in FIG. Further, as shown in FIG. 3C, when the stress concentration resin test piece shown in FIG. 3A is bent at three points, stress is applied to the stress concentration portion in the direction of the arrow. When a load is applied to the L-shaped stress-concentrated resin test piece as shown in FIG. 4A in the direction of the white arrow in FIG. 4B, the stress is concentrated in the direction indicated by the arrow. It takes. As described above, the stress generated in the stress concentration portion varies depending on how the predetermined load is applied. Further, as described above, when a load is applied to the stress concentration resin test piece having the stress concentration portion, a large stress is generated in the stress concentration portion.

  As described above, the stress generated in the stress concentration portion varies depending on the type of the stress concentration resin test piece and how to apply the load. Therefore, as will be described later, it is preferable to derive correction coefficients, relational expressions, and the like described later with a plurality of stress-concentrated resin test pieces and a plurality of fracture modes. This is because various resin molded products having a shape stress concentration portion can also be predicted.

  In addition, by considering the stress-concentrated resin test piece as shown in FIGS. 1, 3, and 4 and the fracture mode, it is possible to predict the resin test piece of almost any shape.

  The analysis method is not particularly limited, and may be linear analysis or non-linear analysis. However, the present invention is characterized in that a value extremely close to an actual measurement value can be predicted by correcting a value obtained by a simple analysis such as a linear analysis. Therefore, the analysis in this step is preferably a simpler linear analysis.

[Predictive limit load calculation process]
The predicted limit load calculation step is a step of calculating the predicted limit load by dividing the limit stress using the analysis stress per unit load calculated from the analysis stress. The predicted breaking load here is different from the actual breaking load. If the limit load prediction method of the present invention is used, a limit load closer to actual measurement can be predicted. The object of the present invention is to perform prediction with higher accuracy than the limit load predicted at this stage. The "limit load" refers to the fracture load in the resin material that exhibits the brittle fracture mode, and the yield load in the resin material that exhibits the ductile fracture mode, and means the load at the strength limit of use in the resin material. To do.

[Measurement limit load derivation process]
The actual measurement limit load deriving step is a step of deriving the actual measurement limit load of the stress concentration resin test piece when the stress concentration resin test piece actually breaks. The difference between the predicted limit load and the measured limit load when nonlinear analysis is used in the analysis stress deriving step is smaller than when linear analysis is used. However, nonlinear analysis takes more time than linear analysis. As described above, one of the features of the present invention is that even if linear analysis is used in the analysis step, the predicted value can be corrected so that it finally approaches the actual measurement value.

[Correction coefficient derivation process]
The correction coefficient deriving step is a step of obtaining a correction coefficient by dividing the predicted limit load obtained in the predicted limit load calculating step using the actually measured limit load obtained in the measured limit load deriving step. The correction coefficient is a value for making the analysis value an actual measurement value by multiplying the analysis stress or a value for bringing the analysis value close to the actual measurement value.

[Correlation derivation process]
The correlation derivation step is to change the type of the resin material and / or the predetermined surrounding environment, and perform the step of obtaining the correction factor at least once in the same manner as the correction factor derivation step. Is a step of deriving the correlation between the two by a function of a predetermined format. One of the features of the present invention is that it has been found that there is a correlation between the breaking strain and the correction coefficient, which can be derived by a function of a predetermined format.

  “Similar to the correction coefficient deriving step” refers to changing the conditions such as the type of the resin material and performing the process from the above-described limit stress deriving step to the correction coefficient deriving step.

  FIG. 5 shows the relationship between the breaking strain and the correction coefficient. The vertical axis is the correction coefficient, and the horizontal axis is the breaking strain. Point A is a point showing the relationship between the correction coefficient obtained in the correction coefficient deriving step and the breaking strain obtained in the breaking strain deriving step. Point B is a point indicating the relationship between the correction coefficient and the fracture strain obtained by changing the resin material or the predetermined ambient environment and performing the above-described critical stress derivation process to the correction coefficient derivation process.

  If the conditions are changed as described above and two types of relationship between the correction coefficient and the breaking strain can be derived, the correlation between the breaking strain and the correction coefficient can be expressed by a function of a predetermined format. Therefore, in order to obtain the correlation between the fracture strain and the correction coefficient, it is necessary to obtain the correction coefficient at least once by changing the type of the resin material and / or a predetermined ambient environment.

An approximate function of a predetermined format is obtained by fitting a function of a predetermined format to the points A and B shown in FIG. The form of the approximation function is not particularly limited, and examples include power approximation, logarithmic approximation, linear approximation, polynomial approximation, and exponential approximation. In order to appropriately represent the relationship between the correction coefficient and the breaking strain, power approximation is preferable. FIG. 5 shows a power approximation function (y = ax− ⁿ (y is a correction coefficient, x is a fracture strain, a is a coefficient, and n is a constant)) that represents the relationship between the correction coefficient and the fracture strain. The function is y = a ₁ x ⁻ⁿ¹ (y is a correction coefficient, x is a breaking strain, a ₁ is a coefficient, and n1 is a constant).

  In order to express the relationship between the breaking strain and the correction coefficient by a more appropriate function of a predetermined format, it is preferable to obtain more correction coefficients. Specifically, if seven or more correction coefficients are obtained, a more appropriate function can be derived.

[Multiple correlation derivation process]
The multiple correlation deriving step is a step of changing the curvature radius and performing the step of deriving the correlation with the function of the predetermined format at least once in the same manner as the correlation deriving step. Although this step is not an essential step, the estimated correction factor can be determined more accurately by obtaining more relationships between the correction factor and the fracture strain, and the prediction accuracy is further improved.

[Relationship derivation process]
The relational expression deriving step is a step of deriving a relationship between a constant and a radius of curvature in the function of the predetermined format. The derivation method is not particularly limited, but a method of obtaining based on more correlations is preferable. Note that the relational expression derivation step is not an essential process, but using the relational expression derived in this step increases the accuracy of prediction as will be described later.

The curvature radius is changed, and the process from the critical stress derivation process to the correlation derivation process is performed to derive the correlation between the correction coefficient and the fracture strain. In addition to the above _y = ^{a 1 x -n1} 6, further _y = ^{a 2 x -n2} _(y correction coefficient, x is from breaking strain, _{a 2} is the coefficient representing the n2 is constant) derived Is done. Here, the correlation between the correction coefficient and the breaking strain needs to be in the same form as the approximate function derived in the correlation deriving step. In this step, it is necessary to prepare the functions in order to obtain the relationship between the coefficients (a ₁ , a ₂ ), constants (n ₁ , n ₂ ) and the radius of curvature (R) of the function in a predetermined format. It is.

FIG. 7A shows the relationship between the coefficient a and the radius of curvature (R). The target relational expression of this process is derived by approximating a function of a predetermined form. The predetermined format is not particularly limited as in the case of the above correlation derivation step, but it is preferable to approximate the power function. This is because a more appropriate relationship can be derived. Let the derived function be a = c ₁ R ^d1 (R is a radius of curvature, and c ₁ and d ₁ are constants).

FIG. 7B shows the relationship between the constant n and the radius of curvature. The target relational expression of this process is derived by approximating a function of a predetermined form. It is preferable to approximate a power function as in the case of the relationship between the coefficient a and the radius of curvature. Let the derived function be n = c ₂ R ^−d2 (R is a radius of curvature, and c ₂ and d ₂ are constants).

  As described above, in order to more accurately determine the relationship between the constant of a function of a predetermined format and the radius of curvature, it is preferable to derive three or more functions of a predetermined format representing the relationship between the correction coefficient and the fracture strain. .

[Estimated correction coefficient determination process]
The estimated correction coefficient determination step is a step of determining an estimated correction coefficient using the correlation between the correction coefficient and the fracture strain based on the fracture strain and the radius of curvature. In this step, first, the radius of curvature of the stress concentration portion of the resin molded product having the stress concentration portion as a target is measured. The measurement can be performed by a conventionally known method. After the measurement, the estimated correction coefficient is determined from the correlation between the correction coefficient and the fracture strain. At this time, if a plurality of correlations are obtained, it is possible to determine an estimated correction coefficient with higher accuracy. The breaking strain is determined when the resin material and temperature are determined. The breaking strain may be measured by a conventionally known method, or the value can be used when it can be obtained from a catalog or the like.

When the relationship between a constant of a function of a predetermined format and the radius of curvature is obtained, the coefficient a is obtained by substituting the radius of curvature into the relational expression a = c ₁ R ^d1 . Next, the coefficient n is obtained by substituting the radius of curvature into n = c ₂ R ^−d2 . Then, the relationship between the breaking strain and the correction coefficient is obtained. Finally, the value of the breaking strain is substituted into the relational expression between the breaking strain and the correction coefficient, and the correction coefficient is estimated. By determining the estimated correction coefficient in this way, the estimated correction coefficient becomes more accurate and the accuracy of prediction increases.

[Generating stress prediction process]
The generated stress prediction step is a resin molded product having a shape stress concentration portion by multiplying the estimated stress by the analysis stress when a desired load is applied to the resin molded product having a shape stress concentration portion. This is a step of predicting the stress generated in the stress concentration part. The radius of curvature of the stress-concentrated portion varies until a load is applied to the resin molded product in the pulling direction and the resin is bent. However, in the linear analysis, since a change in the radius of curvature cannot be considered, a stress value larger than the actual stress value is predicted as the generated stress. The generated stress that can be predicted in the present invention is a stress generated in the stress concentration portion when it is assumed that the stress concentration portion is deformed from application of a desired load to fracture.

  Conventionally, since the point of change in the radius of curvature of the stress-concentrated portion between the time when a load was applied to the resin molded product and failure could not be taken into account, the prediction based on the analytical stress is Only very different predictions could be made. However, in the present invention, it is possible to approximate the actual measurement by multiplying the analytical stress by the correction coefficient, and it is possible to predict the stress generated in the stress concentration portion very accurately.

  The stress generated in the stress concentration portion differs depending on the type of stress concentration resin test piece and how to apply the load. Therefore, in order to apply to a wide variety of resin molded products, it is necessary to obtain a correlation for each type of stress concentration portion. In order to cope with various resin molded products having a shape stress concentration portion, as shown in FIG. 3A, a stress concentration resin test piece provided with notches on both sides as shown in FIG. 1 (b), FIG. 3 (b), (c), a stress concentration resin test piece provided with a notch on one side, and an L-type stress concentration resin test piece as shown in FIG. It is necessary to derive a correlation for each destruction mode as shown in FIG. Considering the stress concentration resin test piece and the fracture mode as described above, various resin molded products having a shape stress concentration portion can be handled.

  Specifically, as shown in FIG. 8, the relationship between the radius of curvature and the correction coefficient in each destruction mode can be expressed. If the curvature radii are the same, the correction coefficient in the case of the fracture mode shown in FIG. 4B using an L-shaped stress concentration test piece is the highest, and the next highest is as shown in FIG. 3C. This is a three-point bending, and the third largest is a fracture mode as shown in FIG. 1 (b) in which a test piece with notches on both sides is pulled, and the correction coefficient is the smallest. This is a mode in which a stress-concentrated resin test piece having a notch only on one side as shown in FIG. As described above, since the correction coefficient differs depending on the fracture mode, it is necessary to derive a correlation between the fracture strain and the correction coefficient for each fracture mode and to derive a final relational expression.

[Limit load prediction process]
The limit load prediction step is a step of calculating the limit load of the resin molded product by dividing the limit stress by the generated stress predicted in the generated stress prediction step and multiplying by the desired load. As described above, since the point that the radius of curvature of the stress concentration part changes between the time when a load is applied to the resin molded product and the failure has not been considered in the past, In some cases, there was a big difference in prediction. However, since the present invention predicts taking into account the above-described change in the radius of curvature, a value closer to actual measurement can be predicted.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Resin material>
Polyacetal resin 1: Duracon M90 (manufactured by Polyplastics)
Polyacetal resin 2: Duracon GH-25 (manufactured by Polyplastics)
Polybutylene terephthalate resin 1: DURANEX 2002 (manufactured by Wintech Polymer)
Polybutylene terephthalate resin 2: DURANEX 3300 (manufactured by Wintech Polymer)
Polyphenylene sulfide resin 1: Fortron 0220A9 (manufactured by Polyplastics)
Polyphenylene sulfide resin 2: Fortron 1140A1 (manufactured by Polyplastics)
Liquid crystalline resin 1: Vectra A950 (manufactured by Polyplastics)
Liquid crystalline resin 2: Vectra A130 (manufactured by Polyplastics)

<Molding of resin material>
The molding conditions were appropriately adjusted for each resin material, the molding conditions were appropriately adjusted for each resin material, and a stress measurement resin test piece without a stress concentration portion as shown in FIG. 9A was molded by injection molding. Further, an L-shaped resin molded product as shown in FIG. 9B was obtained. Three types of stress-concentrated resin test pieces having a corner radius of curvature (R) of 3.0 mm, 1.0 mm, and 0.5 mm were molded by injection molding.

<Limit stress derivation process>
The critical stress was derived using a stress measurement resin test piece (thickness 4 mm, other dimensions described in FIG. 9C) shown in FIG. 9C molded using the polyacetal resin 1. Specifically, the tester (“Tensilon RTA-250”) was supported by a method in which the ambient environment was 23 ° C. in the atmosphere and supported by a span of 64 mm as shown in FIG. , Manufactured by ORIENTEC Co., Ltd.), the critical stress due to three-point bending was measured (64 mm distance between fulcrums). The limit load was 150 N, and the limit stress (bending strength) was 90 MPa.

<Breaking strain derivation process>
Breaking strain was derived using a stress measurement resin test piece shown in FIG. 9A formed using the polyacetal resin 1. Specifically, both ends of the strain measurement resin test piece were fixed with a chuck to the dotted line portion in FIG. 9 under the condition that the ambient environment was in the atmosphere at 23 ° C. (the distance between chucks was 115 mm), and a tensile tester ("Tensilon RTC-1325", manufactured by ORIENTEC) was used to conduct a tensile test. As a result, the elongation between chucks was 40.2 mm, and the breaking strain was 35%.

<Analysis stress derivation process>
When applying a load of 1 N to the stress concentration test piece (R = 0.5) shown in FIG. 9B molded using the polyacetal resin 1 in the direction indicated by the white arrow shown in FIG. The stress generated in the stress concentration portion (the corner portion of the L-shaped test piece) was analyzed using linear analysis software (“I-DEAS”, manufactured by EDS) to derive the analytical stress. The analytical stress value was 3.79 MPa.

<Predicted limit load calculation process>
By dividing the limit stress of 90 MPa by the analytical stress of 3.79 MPa per unit load, a predicted limit load was obtained. The predicted limit load was 23.7N.

<Measurement limit load derivation process>
FIG. 4B shows a stress concentration test piece (R = 0.5 mm, thickness 3 mm, other dimensions are shown in FIG. 9B) shown in FIG. 9B molded using the polyacetal resin 1. ) Using a tester (“Tensilon RTA-250”, manufactured by ORIENTEC Co., Ltd.) in the direction indicated by the white arrow, the load when the stress-concentrated resin specimen was broken was measured. The measurement result of the limit load was 55.6N.

<Correction coefficient derivation process>
The correction coefficient obtained by dividing the predicted limit load 23.7N by using the actually measured limit load 55.6N was 0.427.

<Correlation derivation process>
A correction coefficient under each condition was obtained in the same manner as in the derivation of the correction coefficient except that the predetermined temperature at the time of measurement or the type of the resin material was changed to each condition shown in the second and subsequent columns of Table 1. An approximate expression y = A ₁ x ⁻ⁿ¹ representing the correlation between the correction coefficient and the breaking strain (y is the correction coefficient, x is the breaking strain, a ₁ is the coefficient, and n 1 is a constant) was obtained. The approximate expression was obtained using calculation software.

<Multiple correlation derivation process / relational expression derivation process>
A correlation was obtained when a stress concentration test piece having a curvature radius of 1.0 was used in the same manner as the derivation of the above correlation except that a test piece having a curvature radius of 1.0 mm was used. Table 1 shows the types of resin materials used and the predetermined temperatures. Moreover, the obtained approximate expression was y = A ₂ x ⁻ⁿ² (y is a correction coefficient, x is a breaking strain, a ₂ is a coefficient, and ⁿ 2 is a constant).

A correlation was obtained when a stress concentration test piece having a curvature radius of 3.0 mm was used in the same manner as the derivation of the above correlation except that a test piece having a curvature radius of 3.0 mm was used. Table 1 shows the types of resin materials used and the predetermined temperatures. Moreover, the obtained approximate expression was y = A ₃ x− ⁿ³ (y is a correction coefficient, x is a breaking strain, a ₃ is a coefficient, and n 3 is a constant).

Approximate function representing the relationship between R and a (the form of the function is a = c ₁ R ^d1 (R is the radius of curvature, c ₁ and d ₁ are constants)) and the approximate function representing the relationship between R and n ( The function format was determined as n = c ₂ R ^−d2 (R is a radius of curvature, and c ₂ and d ₂ are constants). The approximate expression was obtained using calculation software.

<Estimated correction coefficient determination process>
The curvature radius of the stress-concentrated portion of a resin-molded product having a stress-concentrated portion as shown in FIG. 11 formed by molding the polyacetal resin 1 (the unit of dimensions in FIG. 11 is mm) was measured. The curvature radius was 1.0 mm. This curvature radius was substituted into the above approximate function (a = c ₁ R ^d1 , n = c ₂ R ^−d2 ), and a and n were obtained. As a result, an approximate expression representing the correlation between the correction coefficient at the curvature radius of 1.0 mm and the fracture strain was obtained. The fracture strain of the molded product at 23 ° C. in the atmosphere was measured by the same method as in the fracture strain deriving step. The breaking strain was 35%. The correction coefficient was estimated by substituting the breaking strain into an approximate expression representing the correlation between the correction coefficient and the breaking strain. The estimated correction coefficient determined was 0.51.

<Generating stress prediction process>
In the case where a load of 1 N is applied to the resin molded product in the direction indicated by the arrow in FIG. 11, the stress generated in the stress concentration portion (the corner portion of the L-shaped test piece) )) Was used to perform a linear static analysis and the analytical stress was derived. The value of analytical stress was 1.36 MPa. By multiplying this analytical stress by a correction factor of 0.51, the stress generated in the stress concentration portion was predicted. The predicted value of the generated stress was 0.69 MPa.

<Limit load prediction process>
The predicted critical load was obtained by dividing the critical stress of 90 MPa by the predicted generated stress per unit load of 0.69 MPa. The predicted limit load was 130.4N. When the limit load was measured, the obtained limit load was 120N. Therefore, according to the present invention, it was confirmed that the accuracy of predicting the limit load is high.

Claims (9)

A method for predicting a generated stress in a stress-concentrated portion of a resin molded product when a load that breaks the resin-molded product having a shape stress-concentrated portion is applied, and predicting a limit load of the resin molded product having the stress-concentrated portion Because
A limit stress deriving step of deriving a limit stress of the stress measurement resin test piece when a load is applied to a stress measurement resin test piece of a predetermined ambient environment not including a shape stress concentration portion;
Breaking strain derivation step for deriving a breaking strain when a load is applied to the strain measuring resin test piece in a tensile direction with respect to the strain measuring resin test piece at a predetermined temperature not including a stress concentration portion,
An analytical stress deriving step for deriving analytical stress generated in the stress concentration portion by analysis when a predetermined load is applied to a stress concentration resin test piece having a stress concentration portion having a predetermined radius of curvature;
A predictive limit load calculating step of calculating a predictive limit load by dividing the limit stress using the analytical stress per unit load calculated from the analytical stress;
In the stress concentration resin test piece, an actual measurement limit load derivation step for deriving an actual measurement limit load when the stress concentration resin test piece breaks;
A correction coefficient derivation step for obtaining a correction coefficient by dividing the predicted limit load using the measured limit load;
Change the type of the resin material and / or the predetermined ambient environment, and perform the step of obtaining the correction coefficient at least once in the same manner as the correction coefficient derivation step, and the correlation between the fracture strain and the correction coefficient is in a predetermined format. A correlation derivation step derived by a function of
An estimated correction coefficient determining step for determining an estimated correction coefficient based on the correlation between the breaking strain and the correction coefficient, and a limit load prediction method comprising: The limit load prediction method according to claim 1, wherein the function of the predetermined format satisfies the following formula (I).

(In formula (I), y represents a correction coefficient, x represents a breaking strain, a represents a coefficient, and n represents a constant.)   A plurality of correlation deriving steps for changing the radius of curvature and performing the step of deriving the correlation with the function of the predetermined format at least once in the same manner as the correlation deriving step, after the correlation deriving step The limit load prediction method according to claim 1, further comprising a limit load prediction method.   The limit load prediction method according to any one of claims 1 to 3, further comprising a relational expression deriving step for deriving a relation between a constant and a radius of curvature in the function of the predetermined format. The limit load prediction method according to claim 4, wherein a relationship between a constant and a radius of curvature in the function of the predetermined format satisfies the following formulas (II-a) and (II-b).

(In formula (II-a), a is a coefficient, R is a radius of curvature, and c ₁ and d ₁ are constants.)

(In formula (II-b), n is a constant, R is a radius of curvature, and c ₂ and d ₂ are constants.)   6. The stress measurement resin test piece is the same as the strain measurement resin test piece, and the limit stress is derived by applying a load in a tensile direction in the limit stress deriving step. The limit load prediction method described in Crab.   The limit load prediction method according to claim 1, wherein the analysis is a linear analysis. The estimated correction coefficient determination step is a step of calculating an estimated correction coefficient based on the fracture strain and the radius of curvature using the relational expression derived by the method according to claim 4 or 5.
Generated stress that predicts the generated stress generated in the stress concentration part of the resin molded product having a geometric stress concentration part by multiplying the estimated stress by the analytical stress when a desired load is applied to the resin molded product A limit load prediction method, further comprising: a prediction step.   A limit load prediction method, wherein the limit load of the resin molded product is calculated by dividing the limit stress by the generated stress predicted by the method according to claim 8 and multiplying by the desired load.

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